This invention relates generally to systems for producing responses to ambient light which corresponds to the response of a human eye, and more particularly, to a system which is particularly adaptable to the control of headlamps in vehicles in response to changes in the incident ambient light.
Headlamp control systems for use in vehicles, which systems are also known as "twilight sensors," have several shortcomings, most of which are derived from the fact that a known twilight sensor responds differently to ambient light than a human eye. As a result of this different response characteristic, twilight sensors will respond differently than the eye as each is subjected to different lighting conditions.
As an example of the foregoing, assume, for the moment, that a twilight sensor is adjusted to actuate the headlamps of a vehicle at 200 foot-candles under a cloudless sky. Such a setting might cause the headlamps to be turned on at 100 foot-candles on a cloudy day. A foot-candle is a unit of light intensity which takes into account the spectral response of the human eye to light. As is known, the human eye is most sensitive to green light, and therefore less light energy in the form of green light is required to obtain the same response to the eye, as, for example, red light.
One known twilight sensor system employs a blue filter followed by a photoresistive cell, or a photodiode, whereby the light sensor will respond only to blue light. The blue filter is intended to reduce the sensitivity of the twilight sensor to street lights which radiate mostly yellow and red light. Clearly, this known twilight sensor system will not correspond in its operation to the light which is seen by a human eye.
In addition to the foregoing, there is a need in the art to provide to a control unit which controls the operation of a ventilation, heater, or air conditioning unit of a vehicle information pertaining to the location of the sun, with respect to the vehicle. There is available in the prior art a large variety of systems for producing electrical signals having information content responsive to the orientation of a light source, such as the sun, relative to a photodetector. Most of the known arrangements for performing this function are complex and expensive, and also are rather bulky with their associated electronic signal analysis systems. One known arrangement utilizes a pair of solar cells arranged orthogonal to one another. The incident electromagnetic radiation, or sunlight, causes the solar detectors to generate respective output electrical signals having amplitudes responsive to the angle of incidence of the light. Ratio detecting circuitry is used to determine the angle of incidence with respect to the orientation of the solar detectors, by monitoring and comparing the output signals of the respective solar detectors.
A further known system for determining the direction of incident radiation utilizes a sensor head having a hemispherical convex surface area on which are terminated a plurality of optical fibers. The optical fibers are bundled and terminated at their distal ends with detectors, which are arrayed illustratively in the form of a matrix. This known system, however, in addition to requiring a multiplicity of detectors arranged in a matrix, also requires complex mathematical and evaluation circuitry which render this known system unsuitable in applications where simplicity and economy are required.
Particularly in mobile systems which continually are changing their orientation with respect to the sun, it is desirable to modify the output of associated heating and cooling systems so as to take into consideration the effects of sunlight. In such systems, however, there is not often available space for a complex, multi-component sensor and associated computation circuitry. There is, of course, a need for a sensor which is responsive to the position of a light source, and which also is compact and reliable. One known sensor which addresses a number of the problems associated with delivering signals responsive to the relative orientation of the sun is described in U.S. Pat. No. 4,933,550, which issued to the inventor herein on Jun. 12, 1990. This known arrangement, however, does not address the need of current-day vehicles for a unified arrangement which serves the dual purpose of providing to the vehicle's controls systems signals which can be employed to determine the relative orientation of the sun, for controlling ventilation, heating, and air conditioning systems, and also ambient light signals conformed in spectral characteristic to the human eye for controlling the operation of headlamps.
It is, therefore, an object of this invention to provide a system which is responsive to ambient light in accordance with a characteristic which corresponds to that of a human eye and for monitoring the position of a light source, the system being simple and inexpensive.
It is another object of this invention to provide a system for controlling the operation of the headlamps of a vehicle, whereby the headlamps are operated in a manner consistent with the perception of the ambient light by a human operator of the vehicle, wherein the same detector also achieves the function of monitoring the location of the sun.
In addition to the foregoing, there is a need for a combined solar position indicator and twilight sensor, wherein the twilight sensor responds quickly to the rapid changes in the intensity of ambient light, particularly when the ambient light rapidly becomes diminished, as would be the case when a vehicle enters a tunnel. Thus, it is also an object of this invention to provide a twilight sensor arrangement which can respond quickly to actuate the headlamps when the ambient light diminishes rapidly, without responding to electrical noise or transient ambient light.
It is a further object of this invention to provide a combined cooling and headlamp control system for a vehicle wherein it will always appear to the driver that the headlamps are turning on when the sky reaches the same light brightness, wherein the position of the sun is monitored without the need for multi-detector comparator circuitry.
It is additionally an object of this invention to provide a headlamp control system which actuates the headlamps of a vehicle in a manner consistent with the perception of a human eye, irrespective of whether the ambient conditions are clear or cloudy.
It is also another object of this invention to provide a system for monitoring the position of a light source simultaneously with the magnitude of ambient light, wherein a high degree of compactness is achieved.
It is yet an additional object of this invention to provide a combined system for monitoring the position of a light source and the ambient light which conforms to the frequency characteristic of the human eye, the combined system being particularly suited for mobile applications.
It is still another object of this invention to provide an arrangement for controlling a mobile cooling system in response to incident sunlight being within a predetermined range of angles of elevation.
It is yet a further object of this invention to provide an arrangement for controlling a mobile cooling system in response to incident sunlight being within a predetermined range of angles of azimuth.
It is also a further object of this invention to provide an arrangement for controlling a mobile cooling system in response to the angle of incidence of sunlight.